1. Field of the Invention
The invention relates to an arrangement (apparatus) for transferring heating and cooling power by means of two heat transfer heating media, in which arrangement at least one of the heat transfer media is arranged to be evaporated or condensed.
2. The Prior Art
Absorption aggregates have long been used for transferring thermal energy from one energy level to another, or in other words, for producing heating or cooling power on a useful temperature level from a source not on a useful level. The operation of absorption aggregates is based on that possible because specific absorption agents are capable of absorbing to themselves specific other agents at a higher temperature than the boiling point of the agent under the prevailing pressure. In other words, they are able to bind to liquid another vaporous agent at a temperature higher than the boiling point of the agent in question. These agents, i.e., agents forming an absorption pair, can be separated again from one another by raising the temperature, i.e., by boiling.
Today buildings are generally cooled by a cooling aggregate based on a compressor aggregate, the cooling aggregates being dispersed to places of use. Cooling power is produced in them by electricity. The proportion of the cooling of buildings in the consumption of electricity is now fairly important, e.g., in the Southern European countries the electricity consumption peaks in the summer. With regard to production, the consumption also occurs at an unfavourable time. The heat inevitably generated in connection with the production of electricity cannot be used for much else than production of hot tap water, and so it has to be condensed and supplied to waterways, e.g., by brine condensers or to air by cooling towers.
Cooling power could also be produced by waste heat produced in the production of electricity in absorption aggregates mentioned above, the best known of which are lithiumbromide/water and ammonia/water aggregates. The consumption of electricity and thus, e.g., emissions of CO.sub.2 could be reduced with these aggregates, and the waste heat, which is now completely wasted, could be utilized by generating cooling power at a power plant and by distributing it with a pipe system to places of use in the same way as district heat at present, or by utilizing the present district heating network and by generating cooling power in smaller units specifically for each area or building. This has an advantageous effect, e.g., on servicing costs, which in the present, dispersed systems are high, and on reliability, on space utilization in buildings, etc.
Another way to reduce the consumption of electricity is to generate the required heat by solar collectors, the power derived from which is generally at its highest when the need for cooling is at its greatest. If the collector system is dimensioned by the amount of radiation and radiation times in spring/autumn to correspond to the consumption of tap water, there is a lot of extra capacity in mid-summer, which capacity could be used at least to cut the peak power.
Absorption cooling systems have not become common, however, due to high investment costs. Although the kWh price of the chill generated in this way is low as compared with the price of electricity, the number of hours of use is so small in those climatic zones where district heating systems have been built that the investment costs will not be covered. In Finland, for example, such systems have thus not been built. The majority of them exist in Japan, Korea and the U.S.
Another essential factor is the large size of the apparatuses operating on the absorption principle at present. The need for space is triple in comparison with a compressor aggregate, for example, which further raises costs.
The main reasons for the great need for space are heat exchangers connected to a low pressure prevailing in evaporator and absorption parts. If boiling, that is, the separation of the parts of the absorption pair from one another is to be done with district heating water whose temperature in Finland, for example, is generally about 70 to 75.degree. C. in the summer, there is also a low pressure in the boiling and condensation parts. Low pressure vapour flowing in all parts of the absorption aggregate requires large flow paths, which increases the size of the apparatus and especially that of the heat exchangers.
The requirement of large flow paths has meant that it has not been possible to build absorption aggregates in district heating networks for ordinary boiling temperatures of 70 to 80.degree. C. as the size of the aggregate, as well as the costs of the aggregate, will grow too much because of low pressure.
A high boiling temperature is particularly disadvantageous to the use of solar collectors as their power will fall considerably if the temperature of the heat exchange liquid rises.
The requirement of large flow paths has also resulted in that all the absorption aggregates on the market are built by using tube heat exchangers where the ratio of the area of the flow paths and temperature is great and can be selected according to the purpose of use by varying the pipe diameter. Their manufacture costs are, however, high as it is difficult to automatize manufacture, and the price/heat delivery surface-m.sup.2 of the raw material, i.e., of the pipes is high. Furthermore, the raw material consumption/heat delivery surface-m.sup.2 is high as well as the need for space/heat delivery surface-m.sup.2.
Because of the above reasons, plate heat exchangers have in recent years almost replaced tube heat exchangers as liquid/liquid exchangers. The small need for space of the plate heat exchangers has the drawback that the flow paths of the heating medium especially at the comers of the exchanger are very narrow. Because of technical manufacturing reasons, they cannot be made to be very much larger either. Therefore, the plate heat exchanger is best suitable as a liquid/liquid exchanger and for clearly overpressure vapour. A considerably low pressure vapour does not simply have room to flow through narrow flow paths. This explains why plate heat exchangers have not been used in absorption aggregates.
For example, Finnish Patent Specification No. 95414 discloses a plate heat exchanger placed in a container to which a heat transfer medium is conveyed to flow directly to the slots between channel plates. The flowing area can be increased substantially in this way. This kind of a heat exchanger has been applied to the vaporization and condensation apparatus of Finnish Patent Specification No. 95414 where one of the heat transfer media will evaporate and the other condense as in an apparatus, for example, where salt-free water is produced of sea water. The area of the vapour flow path will thus be EQU A=n.times.s.times.a,
where n=the number of slots between the channel plates
s=the width of slots between the channel plates PA1 a=the length of a side of the exchanger. PA1 s=the width of slots between the channel plates PA1 a, b=the length of sides of the exchanger.
The apparatus shown above is not, however, suitable for absorption aggregates, for example, where one of the heat transfer media will evaporate or condense while the other will stay in liquid form.